This project seeks to determine whether chemical carcinogens interacting differently with DNA induce the same or different agent-specific changes in DNA, necessary for malignant transformation of mammalian cells. DNA's of BALB 3T3 cells, transformed by carcinogens of at least three different classes, are transfected into NIH 3T3 cells and mouse epidermal cells permissive for expression of the transformed phenotype. Transforming DNA's produced by each agent will be compared according to efficiency of expression in permissive indicator cells and patterns of sensitivity to restriction endonucleases. Other studies investigate whether apparently recessive suppressor genes are inactivated early in multistage carcinogenesis in order to permit expression of transforming genes. Cell culture and biochemical facilities have been established. Six MNNG-transformed BALB 3T3 cell lines were isolated. BP and 4NQO-transformed BALB 3T3 cell lines were obtained from T. Kakunaga. Successful transfection of NIH 3T3 cells was confirmed under present laboratory conditions using cloned Moloney sarcoma virus transforming genes. Development of a chemically defined culture medium was initiated to improve reproducibility and efficiency of transfection assays.